[changelog] Add changelog for java/v1.0.1

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Protected files were modified in this change.
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Protected files: CHANGELOG.md

Adds the CHANGELOG.md entry for the java/v1.0.1 stable release.

Changes covered (3 user-visible):

• @CopilotExperimental compile-time gate for experimental APIs (Add @CopilotExperimental compile-time gate for experimental APIs #1601)
• Open-canvases snapshot (getOpenCanvases()) on CopilotSession (Add open-canvases snapshot tracking to the Java SDK #1606)
• Schema-driven @Deprecated and experimental @apiNote propagation into generated types (Edburns/ghcp 1573 java ensure zod metadata shows thru #1591)

Generated by Release Changelog Generator · sonnet46 1.8M · ◷

[github-actions]

Protected files were modified in this pull request and require manual scrutiny before merge.

Please verify that each protected-file change is intentional, policy-compliant, and safe:

• Protected files: CHANGELOG.md

[SteveSandersonMS]

We need a better system for updating changelog. This is out of date already.